1. Related Applications
This application is related to co-pending U.S. patent applications:
Ser. No. 07-698,745 now U.S. Pat. No. 5,109,721 entitled RANGE SHIFTING ONLY FAULT TOLERANCE METHOD/SYSTEM;
Ser. No. 07-697,813 now U.S. Pat. No. 5,109,729 entitled THROTTLE CONTROL FAULT DETECTION AND TOLERANCE METHOD/SYSTEM;
Ser. No. 07-697,384 now U.S. Pat. No. 5,099,711 entitled TOOTH BUTT/BUZZ CONTROL METHOD SYSTEM;
Ser. No. 07-698,752 now U.S. Pat. No. 5,136,897 entitled SMOOTH UPSHIFT CONTROL METHOD/SYSTEM;
Ser. No. 07-698,751 now U.S. Pat. No. 5,136,897 entitled COMPOUND POWER DOWNSHIFT METHOD/SYSTEM; and
Ser. No. 07-698,017 entitled DRIVELINE TORQUE LIMIT CONTROL STRATEGY-USING SAE J1922 TYPE ENGINE CONTROL,
all filed the same day, May 9, 1991, and assigned to the same assignee, Eaton Corporation, as this application.
2. Field of the Invention
The present invention relates to a control system and control method for controlling the operation of an automated mechanical transmission system, preferably of the type including an engine, a torque converter, a lock-up/disconnect clutch assembly, a power synchronizer assembly and a mechanical transmission.
In particular, the present invention relates to a control system/method for an automated transmission system as described above wherein the selection of a target gear during power downshifts is a function of several parameters including torque converter slip, vehicle deceleration, throttle position and currently engaged gear ratio.
2. Description of the Prior Art
Mechanical transmission systems of the compound range, splitter or combined range and splitter type are well known in the prior art as may be seen by reference to U.S. Pat. Nos. 4,788,889; 4,754,665 and 4,735,109, the disclosures of which are incorporated by reference.
Automatic mechanical transmission systems comprising mechanical transmissions and controls and actuators to automatically shift same, usually electronically controlled in accordance with sensed inputs and predetermined logic rules, are known. Examples of such systems may be seen by reference to U.S. Pat. Nos. 4,648,290; 4,595,986; 4,527,447; 4,711,141; 4,792,901; 4,361,060; 4,140,031 and 4,081,065, the disclosures of which hereby incorporated by reference. Such systems may also be seen by reference to SAE Paper No. 831776 titled "AUTOMATED MECHANICAL TRANSMISSION CONTROLS", the disclosure of which is hereby incorporated by reference.
Fault tolerance logic routines for automatic transmissions are known as may be seen by reference to U.S. Pat. Nos. 4,922,425; 4,849,899 and 4,899,279, the disclosures of which are hereby incorporated by reference.
Automatic transmission systems including a torque converter drivingly interposed a drive engine and a mechanical change gear transmission and/or including torque converter bypass or lock-up devices are also known as may be seen by reference to U.S. Pat. Nos. 3,593,596; 4,261,216; 4,271,724; 4,351,205 and 4,375,171, the disclosures of which are hereby incorporated by reference.
Automatic mechanical transmission systems utilizing power synchronizer devices, i.e. devices independent of engine speed to provide input shaft braking and acceleration, and not manipulation of engine speed, to synchronize the transmission jaw clutch members are known in the prior art. Examples of such systems may be seen by reference to U.S. Pat. Nos. 3,478,851, 4,023,443; 4,140,031 and 4,614,126, the disclosures of which are hereby incorporated by reference.
Automatic mechanical transmission systems having a power synchronizer and also having a torque converter drivingly interposed a drive engine and the transmission input shaft, and including a torque converter lock-up/disconnect clutch assembly, are known. Examples of such systems may be seen by reference to U.S. Pat. Nos. 4,784,019 and 4,860,861 and S.A.E. Paper No. 881830 entitled "THE EATON CEEMAT (CONVERTER ENHANCED ELECTRONICALLY MANAGED AUTOMATIC TRANSMISSION)", the disclosures of which are hereby incorporated by reference.
Such transmission systems provide an automatic mechanical transmission system utilizing a mechanical change gear transmission of a structure identical or substantially identical to the structure of transmissions intended for manual usage, providing the advantages of a torque converter for vehicle start-ups and the advantages of nonslipping connection between the engine and transmission at higher vehicle speeds/gear ratios and providing relatively rapid synchronization of the transmission positive jaw clutches. By providing an automatic mechanical transmission system based upon the same, or substantially the same, mechanical change gear transmission utilized for manual transmission systems, manufacturing, inventory and maintenance cost savings are obtained. To the transmission is added, if necessary, shifting mechanisms suitable for automatic control by solenoids or the like. An example of such a shifting mechanism may be seen by reference to above-mentioned U.S. Pat. Nos. 4,361,060 and 4,899,607 and U.S. Pat. Nos. 4,873,881; 4,722,237; and 4,445,393, the disclosures of which are hereby incorporated by reference. A power synchronizer mechanism as disclosed in above-mentioned U.S. Pat. Nos. 4,614,126; 3,478,851 or 4,023,443 is also added for synchronizing the transmission positive jaw clutches.
A torque converter is drivingly interposed the drive engine and transmission. A torque converter lock-up and disconnect clutch structure is provided comprising a first and a second separate, independently operable, clutches, preferably friction clutches, for coupling the torque converter driven member or turbine to the transmission input shaft and for coupling the torque converter input or impeller (i.e. the engine output) to the transmission input shaft, respectively.
The torque converter is drivingly interconnected between the engine and transmission only when the first coupling is engaged and the second disengaged. The torque converter is locked-up, i.e. the turbine driven directly by the engine, when the second clutch is engaged. The transmission is driven directly from the engine, whenever the second clutch is engaged simultaneously with the first clutch.
When the first coupling is disengaged, regardless of the condition of the second coupling, the transmission input shaft is disconnected from the engine torque and also from the inertia of the torque converter and from the inertia of the second coupling allowing the jaw clutches to be easily disengaged, the power synchronizer mechanism to act quickly due to relatively low inertia on the input shaft and also allowing a selected gear to be pre-engaged with the vehicle at rest and in the drive condition.
Electronic and other engine fuel control systems wherein the fuel supplied to the engine may be modulated to provide a desired engine speed, regardless of the operators setting of the throttle pedal, are known in the prior art. Such systems may be seen by reference to above-mentioned U.S. Pat. Nos. 4,081,065; 4,361,060 and 4,792,901 and by reference to the SAE J1922 electronic engine control standards and related standards SAE J1708, J1587 and J1843, the disclosures of which are incorporated herein by reference.
With automated transmission systems of the type described, i.e. derived from a manual mechanical transmission which must interrupt torque during a shift, a primary objective of the control system is to minimize the torque interrupt period, especially during power downshift conditions. Therefore the control strategy must determine a proper gear ratio (i.e. target gear) prior to committing to a shift such that unnecessary additional shifting can be minimized, which may result in a transmission skip power downshift.
Automated mechanical transmission systems having skip downshift logic routines are known in the Prior art as may be seen by reference to U.S. Pat. Nos. 4,576,065, 4,852,006 and 4,916,979, the disclosures of which are incorporated by reference and by reference to above-mentioned S.A.E. Paper No. 831776.